Chabazite, which has the crystal structure designated “CHA”, is a natural zeolite with the approximate formula Ca6Al12Si24O72. Synthetic forms of chabazite are described in “Zeolite Molecular Sieves” by D. W. Breck, published in 1973 by John Wiley & Sons. The synthetic forms reported by Breck are: zeolite “K-G”, described in J. Chem. Soc., p. 2822 (1956), Barrer et al.; zeolite D, described in British Patent No. 868,846 (1961); and zeolite R, described in U.S. Pat. No. 3,030,181, issued Apr. 17, 1962 to Milton. Chabazite is also discussed in “Atlas of Zeolite Structure Types” (1978) by W. H. Meier and D. H. Olson.
The K-G zeolite material reported in the J. Chem. Soc. Article by Barrer et al. is a potassium form having a silica:alumina mole ratio (referred to herein as “SAR”) of 2.3:1 to 4.15:1. Zeolite D reported in British Patent No. 868,846 is a sodium-potassium form having a SAR of 4.5:1 to 4.9:1. Zeolite R reported in U.S. Pat. No. 3,030,181 is a sodium form which has a SAR of 3.45:1 to 3.65:1.
Citation No. 93:66052y in Volume 93 (1980) of Chemical Abstracts concerns a Russian language article by Tsitsishrili et al. in Soobsch. Akad. Nauk. Gruz. SSR 1980, 97(3) 621–4. This article teaches that the presence of tetramethylammonium ions in a reaction mixture containing K2O—Na2O—SiO2—Al2O3—H2O promotes the crystallization of chabazite. The zeolite obtained by the crystallization procedure has a SAR of 4.23.
The molecular sieve designated SSZ-13, which has the CHA crystal structure, is disclosed in U.S. Pat. No. 4,544,538, issued Oct. 1, 1985 to Zones. SSZ-13 is prepared from nitrogen-containing cations derived from 1-adamantamine, 3-quinuclidinol and 2-exo-aminonorbornane. Zones discloses that the SSZ-13 of U.S. Pat. No. 4,544,538 has a composition, as-synthesized and in the anhydrous state, in terms of mole ratios of oxides as follows:(0.5 to 1.4)R2O:(0 to 0.5)M2O:W2O3:(greater than 5)YO2 wherein M is an alkali metal cation, W is selected from aluminum, gallium and mixtures thereof, Y is selected from silicon, germanium and mixtures thereof, and R is an organic cation. As prepared, the silica:alumina mole ratio is typically in the range of 8:1 to about 50:1, higher mole ratios can be obtained by varying the relative ratios of reactants. It is disclosed that higher mole ratios can also be obtained by treating the SSZ-13 with chelating agents or acids to extract aluminum from the SSZ-13 lattice. It is further stated that the silica:alumina mole ratio can also be increased by using silicon and carbon halides and similar compounds.
U.S. Pat. No. 4,544,538 also discloses that the reaction mixture used to prepare SSZ-13 has a YO2/W2O3 mole ratio (e.g., SAR) in the range of 5:1 to 350:1. It is disclosed that use of an aqueous colloidal suspension of silica in the reaction mixture to provide a silica source allows production of SSZ-13 having a relatively high silica:alumina mole ratio.
U.S. Pat. No. 4,544,538 does not, however, disclose SSZ-13 having a silica:alumina mole ratio greater than 50.
U.S. Pat. No. 6,709,644, issued Mar. 23, 2004 to Zones et al., discloses aluminosilicate zeolites having the CHA crystal structure and having small crystallite sizes (designated SSZ-62). The reaction mixture used to prepare SSZ-62 has a SiO2/Al2O3 mole ratio of 20–50. It is disclosed that the zeolite can be used for separation of gasses (e.g., separating carbon dioxide from natural gas), and in catalysts used for the reduction of oxides of nitrogen in a gas stream.(e.g., automotive exhaust), converting lower alcohols and other oxygenated hydrocarbons to liquid products, and for producing dimethylamine.
M. A. Camblor, L. A. Villaescusa and M. J. Diaz-Cabanas, “Synthesis of All-Silica and High-Silica Molecular Sieves in Fluoride Media”, Topics in Catalysis, 9 (1999), pp. 59–76 discloses a method for making all-silica or high-silica zeolites, including chabazite. The chabazite is made in a reaction mixture containing fluoride and a N,N,N-trimethyl-1-adamantammonium structure directing agent. Camblor et al. does not, however, disclose the synthesis of all-or high-silica chabazite from a hydroxide-containing reaction mixture.